Electronic control system for a d.-c. motor



A119 13 l957 w. s. HARVEY E-rm.

ELECTRONIC CONTROL SYSTEM FOR A D-C MOTOR Filed Feb. 28', 1956 LII NWQW IIY CONTROL SYSTEM FOR A D.C. MOTOR Winston S. Harvey, Bedford, and Henry Eisler, Brighton, Mass., assignors to Raytheon Manufacturing Company, kWaltham, Mass., a corporation of Delaware Application February 28, 1956, Serial No. 568,353Y

7 claims. (ci. 31e-33s) ELECTRONIC This invention relates to an electronic control system for controlling a D.C. motor, and` particularly to a system wherein the speed range of the motor can be controlled by therelationship between the field and armature voltages.

. CertainDfC. motors are capable of operating over a widerange of speeds by controlling the relationship between the shunt eld and armature voltages. Such D.C. motors are usually energized initially by the application of the rated value of shunt field voltage while the armature` voltage is increased to its rated value to attain increasing speeds. Thereafter, the armature voltage is maintained at` its, rated value ywhile the shunt eld voltage is decreased to attain increasing speeds.

- The range of speeds characterized by developing the ratedgshunt iield voltage and an increasing armature voltage is` commonly referred to as the constant torque range of the particularniotor. The range of speeds characterized by developing the yrated armature voltage vanda decreasing shunt tieldvoltage is commonly referred to as'l the constant horsepower range.

Pursuant to this invention, a pair of arc-type thyratrons is employed to develop the rated eld voltage overV the constant Ytorque range of speeds. Similarly, a pair of arc-type thyratrons is employed to develop the rated I speed control, in order to obtain smooth transition from,

one speed range to another.

. The speed control is a dual potentiometer which controls the values of armature and eld voltage that can be developed. In the constant torque range, armature voltages less than the rated value are developed. In this range of speeds, the shunt field voltage developed remains constant at the rated value. However, when the speed control is advanced and the D.C. motor is to be operated at speeds in the constant horsepower range, itis necessary to decrease the value of shunt eld voltage developed in order to attain such speeds. A phase-shift circuit is einployed to delay the ring of one of the thyratrons developing said shunt field voltage. Said phase-shift circuit becomes operative to delay the tiring of one of said thyratrons substantially in the vicinity of the constant horsepower range of speed. The phase-shift circuit includes a capacitor and variable resistor connected in series with each other and connected across a center-tapped alternating current supply that makes a grid of each thyratron positive when the corresponding anode is positive, thus causing one thyratron to tire on each half cycle. However, in the constant horsepower range, the lagging phaseshifted voltage is coupled to the grid of one thyratron. Said thyratron tires only over a portion of its conductive half cycle while the other tires normally. In this manner, the generated shunt tield voltage is maintained at a value commensurate with the speed selected for thev motor. Smooth transition from one range of speedsto another is accomplished by selecting particular characteristics for the two-ganged potentiometers comprising the speed control. The armature control section of the speed control is selected so that for a rst sector of rotation,l the constant torque range, its resistanceincreases, causirigsubstantially more armature voltage to be developed. Substantiallyiat' the end of this first sector, the rated value of armature n voltage is generated, but any further rotation of said control does notresult in'any appreciable changey of resistance and the armature voltage remains at the rated The ie'ld control section of the speed control n value. n which forms part ofthe variable resistance of the phaseshift circuit has operating characteristics opposite to those. of the armature control section. Over, the `iirst sector of rotation by the speed control, no yappreciable change of resistance occurs and the tiring time of kone of said thyratrons is not affected. Substantially at the end of the iirst sector and thereafter, the value vof the resistance in the phase-shift circuit increases, causing one of the thyratrons to tire later with increasing speed settings of the speed control. VIn this manner, smooth transition from one range of speed ftoanother is attained.

Heretofore, saturable reactors and associated circuitry' for developing the required D.C. voltages for operating same have been employed to limit the conduction of one or both thyratronsgenerating the shuntk iield voltage; The use of such devices requires more intricate circuitry and necessarily raises the' expenditures forj developing an electronic control. system as described herein.

been obviated by the simple arrangement of the phaseshift circuit in conjunction with the armature control; Q

Another feature of the present invention is theuse of a sensing circuit to monitor the instantaneous magnitude of the armature' voltage in order to limit the magnitude of the shunt eld voltage when the former voltage ywould be excessive. This sensing circuit is the armature overvoltage circuit. It prevents damage to the armature commutators and brushes during periods `when the speed` of the motor is changed substantially. Said circuit biases considering the merit of the invention inaccomplishing this objective. f t

Provision is also made for preventing the motor from being energized or for deenergizing the motor once it has been energized if for any reason the shunt iield voltage is below a predetermined minimum value.``

The aforementioned and other aspects of the invention' will be understood more clearly from the following description of exempliications thereof with reference being made to the accompanying drawing, wherein: t

Fig. 1 is a schematic diagram of an embodiment of the invention for controlling the speed of a 'D.C. motor;

' and Fig. 2 is a graphical representation of the values of` shunt field and armature voltage for the speed ranges core transformer 12. A lcrystal diode 13 in series with resistors 14 and 15, across asecondary winding 16 of the transformer 12, and a capacitor 17, shunt connected4 across the resistors 14 and 15, form a biasingcircuitfor a pair, of arc-type discharge tubes 18 and 19. A' pair ci In the` present invention, the useof these reactor deviceshasy normally-open contacts of a time delay relay 21 is connected between a center tap 22 of the secondary winding 16 and a junction 23 of the resistors 14 and 15. The

junction 23 is connected to a grid 24 or 25 ofthe tubes' 18 and 19 through a pair of normally-closed contacts 26er 27 of a speed-sensitive relay 28 and a currentelimit- Ling resistor 29 or 38. VA pair of normally-open contacts 31 'of the relayV 28 has one contact `attached to the juncv tion of the secondary winding 16 and the cathodeof thek diode 13 and the other contact thereof attached to the.

input side of the resistor 29. A phase-shift circuit 32 secondary winding 16 of the transformer 12.

of thecapacitor 33 and one side .of the potentiometers 34 and 35 is attached to a` contact of a normally-open pair of contacts 39 of the relay 28. The other contact Of the contacts 39 is attached to the inputside of the resistor 30. A solenoid 40V of the relay 21 is attachedto a secondary winding 41 of van iron-core transformer 42.1Y An alternating current supply 43 is` connected across a primary winding44 of the transformer 42.

Cathodes 45 and 46 of the tubes 18 and 19 are connected together. A secondary winding 47 of an ironcore transformer 48 may be connected across the cathodes for heating purposes. ply 49 is connected across afprimary winding50 of the transformer 48. A lead 51 is connected between a center tap 52 of the transformer 48 and the center tap 22 of the secondaryv winding 12. A filter capacitor 53 or 54 is` connected between the grid 24er 25 and the cathode 45I or 46.V An anode 55 or 56 of the tubes 18 and'1-9 is at-l tached to opposite endsV of a center-tappedk secondary winding 57 of an iron-core transformer 58. V An alternating current supply 59' energizes a primary winding 60` of the transformer 58. A center. tap 61 is Yconnected to a common ground 62. Current owing between thel cathodes 45 and 46 and the common ground ows through a variable resistor 63, a shunt ield 64 of the motor employed, and a fuse 65. A slider 66 of the variable resistor 63 is connected to the common ground. The-fuse is connected to the center taps 52 and 22 of the transformers 48 and 12, respectively.' v

Anodes 67 and 68 of another pair of arc-typedischarge tubes 69 and 70 are also connected to opposite ends of the center-tapped secondary winding 57. Cathodes'71 and 72 of said tubes 69 and 70 are connectedA togetherp A secondary winding 73 of an iron-core transformer 74 is connected across the cathodes 71 and 72. VAn alternating current supply '75 energizes a primarywinding 76 of the transformer 74. Grids 77 and 78 of said tubes 69 and 70 are individually connected to cathodes 79 and 80 of another pair of arotype discharge tubes 81 and 82 through capacitors 83 land 84. The tubes 81 and 82 develop positive trigger pulses which are coupled to the grids 77 and 78 and control the tiring time of the tubes 69 and 70. The cathode 79 is connected to the common ground through resistors 162, 8S, and 86. The cathode'80 is connected to the common ground through resistors 163,;vr

87, and 86 in series. The junction of the resistors 85, 86, and 87 is connected to the direct current supply for biasing said -cathodes 79 and 80. Grids 88 and 89 are connectedto opposite ends of -a phase-shift circuit 90 through resistors 91 and 92. Filter capacitors 93' and 94`arexconnected between the grids 88 and 89 and the cathodes 79 and 80. The phase-shift circuit 90 has two parallel legs. VOne leg is comprised of a capacitor 95 in series with a resistor 96. The other leg is comprised of Ia resistor 97 in series with a capacitor 98.`- kThe grid re-y sistor 91 is attached to the junction of the capacitor 95 and the resistor 97.vr The grid: resistor 9.2.is 'attached to,-

An alternating current sup-v y tentiometer 111.

nected'to one Vend ofthe potentiometer 111 while the other end-'of the potentiometer isfconnected to the com\ between the anode 102 and the junction of the resistors' 162 and 85.Y A capacitor 165 is connected between the anode 103 and the junction ofresistors 163 and 87. A centertap 106 of the secondary winding 101 is Vconnected to the common ground. An alternating current supply 107 is connected across a primary winding 108 of the transformer 100,. A center tap 109 of the secondary winding 99 is connected to the wiperarm `110 of a po- A positive D.A C. supply 112i is conmon' ground. The wiperarm 110 of said potentiometer,`

which listhearmature section of the speed control, deter-V mines the firing angleof the'tubes 81 I.and 82 and consequentlyfthering. angle of the tubes 69 and 70.v `The potentiometers '35 and1111 may be tapered or logarithmic? type resistances.- The potentiometers 35 and 111 are connected -into their respective circuits with the wiper arms 37 and 110 ganged, as shown `by line 110A, and the re sistance of.'therpotentiorneter111` increasing` over the first sector of rotation while the resistance of the potentiometer 35'remains negligible. Overthe `second sector of rotation the resistance ofthe potentiometer 35 shouldt increase asthe resistance offthe potentiometer 111re' mains constant. A

Currentlowing between the cathodes 71 and 72 and the grounded "center "tap 61 of the secondary winding 57 flows through an Iarrrlature 113 of the motorzemployed.

Provision is' made for rotating the armature in the for-` ward and reverse directions. In the forward direction the armature hasl one end thereof connected to a center tap` 114 of the secondary Windingv73 through ya pair of normallyfopencontacts 115 of a forward contactor 116. The

other end of the armature isconnected to the common ground-through another'pair of normally-open contacts 117 ofthe forward contactor 116.l In thereverse direc- 'f tion'the -arm-aturehas one end thereof connected to the; center-tap 114l through a pair ofnormally-open contacts 118 of 'areverse contactor 119. The other end of the armature is connected tol the common ground throughY another pair of normally-opencontacts 120 of the reverse contactor-119. In' this manner, the output of the tubes 69 andv` 70 can be switched across the armature.

A solenoid 121 of the forward contactor 116 is ener# gized by an-alternating-current supply 122` when a pair of normally-open contacts 123 ofra forward relay 124 closes. A solenoid 125 of the reverse contactor, 119 is also energized bythe alternating current supply 122 when a pair offnormally-open contacts `126 of aV reverse relay '127 closes. A solenoid v1.28ofthe forward relay 124 hasj one end thereofconnected tothe positive D.C. supply 112.` Similarlygga solenoid 129 of the reverse'relay 127 has one end thereof connected to 1the;positive D.C. supply 112,. The otheriend of the solenoid"'128' is connected to` a normally-closedpair of contacts 130' of a reverse push button 131.@ Similarly,` the other end of the solenoid" 129 isV connectedtoa normally-closed pair o f contacts" 132 of a forward push button 133.` The forward andY reverse push buttons are depressed to energize the cor? responding relay, which in turn energizes the corresponding contacton'whichy causes the' output vof the tubes 69 or 70 to be applied across the appropriate terminals of thev Depressing the forward pushV button 133 f armature. closes apair' of normally-open contacts 134 providing a path'- to ground through a pair of normally-closed con` tacts 135of-astop button inv series to the common ground with apair of normallyopencontacts 136 ofi a iield-lossVA protection relay 137. The function of the eld-loss protection relay and the circuit energizing same will be describedr subsequently.

At this point, it need only be notedthat the forward relay 124 and the reverse relay y127 cannot be energized untilthe contacts 136 close.

Similarly, depressing the reversepush button 131 closes a pair of normally-open contacts 138 providing a path to y the common ground through the stop button 135 and the kcontacts 136.v One contact of the contacts 130 is connected to one contact of the stop button 135 when a pair of normally-open contacts 139 of the forward relay 124 closes. Similarly, one contact of the contacts 132 'is connected to one contact of the stop button 136 when a pair'of normally-open contacts 140 of the reverse relay 127 closes. With this arrangement, once the forward or reverse relay is energized by depressing the particular push button, the relay remains energized after the 'push button is released and until thev stop button is dey The setting of the wiper arm 143` determines the value `of shunt iieldV voltages. The

armature voltage at which the relay 28 becomes energized.y n

A.eldloss protection circuit is employed to prevent the motor from being energized until asufcient amount 'f l of shunt held voltage is developed and, to deenergize the motor once it has been energized if the shunt fieldvoltagek decreases below a minimum value. A portion of rthe shunt field voltage developed across the variable resistor 63 is coupled to thek grid of an electron discharge valve 145`across a resistor 146. The setting 'ofthe slider 66 determines the minimum amount of shunt eld voltage `required to keep the relay 137 energized. A filter capacitor 147 is connected between the grid of the valve 145 and the common ground. Acathode of said valve is connected to the common ground through a load resistor 148. An anode of said valve has as its load a solenoid 149 of the iield-loss protection relay 137. A gaseous voltage regulator 150, having an anode connected between one end of the solenoid 149 and the direct current supply 112 and a cathode connected to the input to the grid of the valve 145, maintains the anode of the valve 145 at positive l5() volts Withrespect to said grid. A resistor 151, connected between the positive 150 volt supply and the cathode of said valve 145, forms a voltage divider to ground with the resistor 148 inthe cathode circuit.

, An armature over-voltage circuit is employed to limit the shunt iield voltage during periods when the armature voltage would be excessive. A portion of the armaturevoltage developed atthe center tap 114 is coupled tothe grid of an electron discharge valve 152 across a voltage divider comprised of a resistor 153 in series to supply, forms a voltage divider for biasing said cathode.

An'anode of said valve 152 is connected to the positive D.C. supply 112 through a resistor 158. The anode is also connected to a cathode of an electron discharge `'valve 159. An anode of the valve 159 is connectedto the grid 24 of the tube'18 through a load resistor 160.

y A capacitor 161 is connected between the anode of said y valve 159. and the center tap 52 of the secondary wind-y ing 47.

' The tubes 18k and 19 are normally nonconducting to y allow the heating of the iilament circuits prior to the to the cathodes at the center tap 52. The connection thepurpose ofjexplanation,r assume that the anode 55 is made negative for a half cycle while the anode`56 is made positive by the connection to the secondary winding 57. Also assume that the vsecondary winding 16 is in phase with the secondary winding 57 so that the cathode of the diode 13 is negative. The 'diode will pass current during this half ycycle andL the current owing through resistors 14 and 15 'will charge the side of the resistor 15 attached to the junction 23 negative. `Since the resistor 15 is, in etfect, connected between the cath-- odes and the grids of the tubes y18 andk 19, the' grid 25 will -be connected to. this knegative potential through the closed contacts 27 and the resistor 30. Thus, when the anode 56 is positive, the tube 19 will not re. On the next half cycle,`th e anode 55 and thevcathode of the dif n ode 13 will bepositive. yThe diode will not conduct on" t A this `half cycle but the capacitor 17 will tend todischarge through the resistors 14 and 15 and keep the side of the' i resistor 15 connected to the junction 23 negative. n The grid124 is connected to this negative potential through the closed contacts 26 and the resistor 29. Thus, when they anode 45 is positive, the tube 18 will not re. The ca-y pacitor 17 maintains the biasing voltage more nearlylike pure D.C. by charging toward the applied voltage across the secondary winding 16 and by discharging only slightly through the resistors 14 and 15 when the diode 13 is nonconducting. The time delay relay 21 is energized after the elapse or" a few minutes. After the contacts20 close,

current4 ceases to flow through `theres'is'tor 15 yso ,that y Thus,`

field voltage in the shuntleld 64. `The fuse 65 is a protective device between the shunt ield and the return path between the center taps 52 and 22 keeps the grid-to-cathode potential constant with variations ofthe shunt field voltage. With the proper selection of `circuit components and voltages, the tubes 18 and 19 cany furnish the rated value of shunt eld voltage for the yD.C. motor employed, and the motor can be energized with the ratedy shunt eld voltage applied and onlyv a small armature voltage. This is a desirable starting condition since large currents are not developed in the armature of the motor. v n

The field-loss protection circuit monitorsthe shunt'eld voltage developed. Any time the value falls below a mini nnum value, the protection circuit prevents the motori-rom y being energized initially or ydeenergiz'es the motor afterit has been energized. The theoryrof operation of said prof f tection circuit is givenfin ak subsequent paragraph.

The tubes 69 and 7i) develop `the voltage for the arma-k ture 113. The tubes 69 and 70 are fired by positive pulses i developed at the cathodes 79 and 80 of the tubes 81 `and 82 and fed to the grids 77 and 78 during the half cycle` the opposite ends of the secondary windingf101.` Simk ilarly, the grids '88 and S9are energized 180 degrees out of phase with respect to each other by the connection of the secondary winding 99 to the junction of the resistor 97 and the capacitor 98 and the junction of the capacitor 95- and the resistor 96. However, the A.C. voltages applied tothe grids i88K and 89 A`are'phase shifted by 9 0 degrees by;r t

I biasing .circuit comprised of. the'diode 13, the 'resistors 14 and 15, and capacitor 17k maintains the grid voltages of the tubes 18 and 19 be-` low the critical voltage necessary to re said tubes vuntil the contacts 20 ofthe time` delay relay 21 close. `For Y'positive half cycle of the anodes.

anode voltages by 90 degrees. the wiper armllt), the armature control, supplies aposit tive D-C.`voltage to the grids S8 and 89 The magnitude of the`D.- C. voltage controls the period during the half..

cycle when the anodes 102 and 103 are positive that the grid vol-tages will exceed the critical voltages necessary to tire the tubes81 and S2. The minimum value ofDf-C.I

voltage that can be coupled to said grids 88- and 39`is adjusted so that the tubes 31 and 82 iire latein thepositive half cycle of the anodes. The maximum value of the D.C. voltage thatcan be coupled to'said gridsSS- and 89 is adjusted so that the tubes 31 Vand 82 tire early'in the When the tubes fire, the capacitors 164 and 165 discharge through said tubes and Ydevelop positive pulses across the resistors 162 and 163. These pulses are coupled across Ithe'capacitors V83 and 84 to the grids 77 and 78. The circuit components and voltages employed for triggering the tubes 81 and 82 have been adjusted so that the positive pulses developed;

at the maximum D.C. voltage setting of the' armature controlwill cause the rated value of armature voltage to be developed.

The tubes 69 and 70 develop the voltage for the arma-`v ture 113. v The anodes 67 and 68 are energized '.180 degrees out of phase by their connection to the centertappedv secondary winding 57. The tubes 69 and 70 are fired evelyhalf cycle, when said anodes are positive, by the positive pulses fed to the grids 77 and 78.Y Since the anodes 67 and 63 are in phase with the anodes 102 and 103 'of the tubesV S1 and 82, said tubes'69 and 70 are fired relatively at the same portion of the positive anode half cycle 'as said tubes S1 and S2. y setting of the speed control, the wiper arm 11G, determines the. firing time of the tubesf69`and 7 0, and thus the amount of armature voltage developed. Withthe particular D.C.

motor employed herein, in the'constant torque range of speeds the armature voltage is an increasing value with speed. In the constant horsepower range'of speeds, the armature voltage remains constant at the rated value.

Thus, the positive pulses fed to the tubes 69 and '70 are n adjusted to arrive earlier in time with increased speed settings until the rated armature voltage is developed.

Current iiowing 'from the cathodes 71 and 72 on alternate half cycles to the center-tapped secondary winding 57 of the'transformer 53 provides the voltage for the armature 113. A pair of contactors energized by a pair of relays provides a means for energizing the armature in the forward or reverse directions. In the forward direc tion, a path to the Vcommon ground from the center tap 114 throughone ,end of the armature is provided when the contacts 115 and 117 of the forward contactor 116 close. In the reverse direction, the center tap 114 is grounded through the other side of the armature through the contacts llland 120 ofthe reverse contacter 119.

The solenoids 121 and 125 of the forward and reverse conta-ctors are energized individually by the forwardand reverse relays 124 and 127. Said relays are energized in the following manner and for the purpose of the explanation assume the contacts 136 of the relay 137 are closed. The forward relay 124 is energized when the push button 133 is depressed. A path to ground for the positive D.C. supply 112 through the solenoid 128 of said relay is provided through the push button 131, the contacts 134, the

stop button 135, and the contacts 136. The contacts. 139

It follows then thatthe Ypush button'131'. One end of the solenoid 129. of said relay.'is'groundedyand the contacts 140 and. 126 c1ose.- Y The .closing of the contacts'140 allows' the push' button 131 tober'elease'd without deenergizing the' relay. f The closing, v of Vthe, contacts 1`26results inV energizing the reverse con? tactor'119.byfclosingthe circuit of the alternating supplyf Y122*through-thesolenoid 125. When the reverse con-v tact'or senergizedyfthe armature isfconnectedV to the, common groundthfrough the closed contacts 118 and 120. As mentioned previously, the wiper arms 110 and 37 of the potentiometers"111 and 35 are gangedand said. potentiometersaretapered or have logarithmic resistance functions.V Let us assume once more that the contacts 136'are closed andfthat we are desirous of energizing the Y armature in the forward direction;

The push button 133k is depressed and the wiperarmf 111, the speed control, isset frvsomey low speed. Afterv the delay imposed by the time delay relay 21, the rated shunt iield voltage is applied to the shunt held 64. AThe setting of the speedcontrol has provided the grids 88 and 89 of the Vtubes 81 andSZ with a small positive voltage. so that there isf'considerable delay in the firing of saidl tubesv on alternatehalfl cycles; t Fig. 2 illustratesr'the relationship between shuntkeld vvoltage and armature voltage for various' speeds. As.a-result of this delay, the' v `armature voltagedeveloped by the tubes 69 and 70 will roi 'Y speed ofthe motor.

be asrnall Vvalue andthe low speed selected will result. As the ,speed control is advanced,thetubes 81 and 82 i. and v,69 andf7tblire earlier so that the armature voltage 30.

and the motorspeed areincreasing.

' As r'nentio'ned earlier, thetubes 69`and 70 develop the rated armature voltage at the setting of the wiper arm 110k -whichi Vcouples the most positive voltage to the tubes 81 I and ,82.15 The speed characterized by the development of the rated shunt `ti'eld and armature voltages isreferred to as the basesp'eed., In the vicinity of the'basefspeed, it

causes Vthe resistance'of the'potentiometer 3S to increase as the resistance of potentiometer 111 remains substa'nfl These new conditions will enable the motor' to develop'- speeds in the constant horsepower range. The constant horsepower range is characterized by speeds tially constant.

resulting from the rated armature voltage and decreasing shunt iield voltages. With the particular characteristicsV chosen `for potentiometer 111, any 'further rotation of the speed control, the wiper arm 110, will not result in :any

change of resistancev ot'saidpotentiometer, so that the rated armature voltage will be developed'. However, the resistance of potentiometer 35 will increase as the speed, control is advanced forincreasing speeds since the wiper arms 11@ and 37iare ganged. Y

The relay 28 is energizedsubstantially near the base noid 141 of the relay, smooths A.C. components of the armature voltage coupled to said solenoid. When the Contacts'31j close, the grid 24 of the tube 18 is conynected to one side of the secondary winding 16; When the contacts 39 close, the grid 25 of the tube 19 is connected to the junction 38 of the phase-shift circuit. The

` tube 18 fires normally over each half cycle when the gridV 24 and the anode 55 are positive. VThe ring of the tube wiper arm 36 of the potentiometer 34, connected in par- V allel with the., potentiometer 35, adjusts Ithe maximum re lsistanceof the parallelfcircuit, and thus determines' the maximum phaseV shiftthatcan be obtained' by rotation of the wiper arm 37 of the potentiometer 35.` The particular'` arrangement of components comprising the phaseshift circuitare such as to enable the voltage applied The wiper arm 1413 of the poten-k tiometer 144 is pressetY tohave this condition occur. They lter capacitor 142, connectedy in shunt with lthe soleto the' grid 25 to be delayed almost 180 degrees. Let us assume that the speed control, the wiper arm 110, has

'been advanced to a position which causes the voltage applied to the grid 25 to be delayed 45 degrees. The tube`18 fires normally when its grid and anode are positiveybut since the firing ofA thetube 18 is delayed by y45 `degrees and the shunt field 64 is a highly inductive 1oad,^t`he tube 18 continues to conduct after its anode has ceased to be positive and is becoming negative. When the lalternating voltagersupplied to the anode 55 of the tube 18 starts to become negative, the'induced voltage in the field maintains the same anode-to-cathode polarity y and the tube 18 continues to conduct until the anode ypotential is more negative than the cathode.

A substantially larger ratio of inductance to D.C. resistance of theinductive load enables shunt field current to fiow uninterrupted until the tube 19 fires. After the 45 deygreedelay, tube 19 fires and shunt field current flows during the remainder of the period during which the n anode'56 is positive and for only a short period theref The-operation of the D.C. motor'necessarily requires changes of speed commensurateV with the use of the motor. I`f-gthe motor is operating at a high speed in -the'constant horsepower range, and the speed control is Vturned down for a substantially lower speed, the tubes 18' and 19 would tend to develop a higher or the rated shuntfield voltage.

Ifthe shunt iield voltage was developed rimmediately for the new setting `of the speed control, the armature voltage would be excessive, andfdainage to the commutator could result.

sinceitsspeed cannot change immediately and respond to the new speed selected. The armature over-voltageprotection circuit maintains the shunt field voltage at a small value until the speed of the motor decreases. l

' mA portionV of the armature voltage at the center'tap 114 of the vsecondary Winding 73 is coupled to the grid of the valve 152 across resistors 153 and 154. Thecapacitorf155 smooths the voltage across the resistor 154. Ifthe armature Voltage is of sufiicient magnitude, the

bias voltage applied to the cathode is yovercome and saidv valve conducts. Let u's assume that the armature voltage is of sufficient magnitude and that this is an instanceV forregulating the amount of shunt field voltage.

thevalve 152 conducts, its'anode and the cathode of the' diode`159 become less positive.. The anode ofthe diode:

When

159,.tends to become more positive since it is attached tothe `grid 24 and the tubes 18 and 19 aref-ending to`v generate a,higher shunt field VoltageV because the speed control has been'positioned for a slower speed: As soon as the :anode of the diode 159 becomes more positive than the cathode, current flows from said cathode, through the resistors 160 and 29, the contacts 131, and ,to the f common ground. The flow ofvcurrent biases the grid 24 atsome-level commensurate with the instantaneous re-` lationship -between thearmature and shunt field voltages.

As a result, thetube 18 may not fire at all over its normally conducting half cycle or only over a portion thereof.

' rlhe capacitor 161 `lends stability to the protection 'offered` by the over-voltage circuit. The bias developed. at thefV grid 24 is required when the anode 55 and thefgrid 24,`

are becoming positive. However, on the next half cycle the grid 24 is made negative and this potential-would very likely cause the diode 159 to stop conducting. Thus, on the succeeding positive cycle, there would be'no bias available at said grid .24, and the tube 18 would, tire,- uneontrolled and defeat the purpose of. the circuit. 'llwf l The'DfC. motor, during'transition periods ofY this-nature, acts like a generator, rather than a motor,

' velops the shunt 4field voltage to decrease 'the value of i, the`shunt`-lield voltage when the armature voltagefr'night weer? side of capacitor 161 connected yto the anode of the, diode 159 charges negatively when said diode conducts,A and when the diode stops conducting, it dischargesy through the resistors 160 and 29y to the common ground. In this way, the bias is'kept atf the4 grid 24 until the armature voltageireturns to within limits. Thereafter, the required shunt field voltage is developed for the particular speed selected..

The field-loss protection' circuit monitors the shunt field n. voltage yfor the reasonsmentioned previously. A portion of the shunt field voltage developed across'the variable A resistor 63 is coupled to the grid ofthe'valve 145 across the resistor 146. kThe capacitor 147 smooths the A.`C. component of the applied voltage. Sincesad valve is normally cutfoi by the bias yvoltage applied tothe cathode, the contacts 136 -are normally open and the armature circuit cannot be energized, as explained earlierin the description of that circuit, However, if the magnitude 'of the input to the grid of the valve 145is sufcient to overcome the bias, the current flowing through the solenoid 149 causes the rcontacts 136 to close and the armature circuit can be energized. This protection circuit is also effective in deenergizing the armature circuit once it has been energized, if for any reason the shunt field voltage falls below the value required to keep the relay 137 energized. V i

v The invention has disclosed a device for energizing a D.C. motor over speed ranges where the rated shunt field voltage and varying armature voltages are required l and wherethe rated armature voltage and varying shunt f field voltages are required. In addition, a protective armature over-voltage circuitk has beensincluded which uniquely utilizes the grid of onefof the tubes that debe excessive. Another protective circuit prevents the armature voltage from ybeing supplied, if for any reason the yshuntv field voltage falls below a certain minimum value.

It is desired that the principles disclosed with the particular embodiment described herein not be restricted to details of assembly and particular components, since many equivalents will suggest themselves to those skilled in the art. yIt is accordingly desired thatthe appended claims be given a broad interpretation commensurate with the scopeV of the invention Within 'the art.

What is claimed is: K A f l. An electronic control system for a 'D.C. motor cornprising electronic means forgenerating the rated Value of D.C. voltage for 4a field winding of a D.C.' motor, electronic means for generating the rated Value D.C. voltage f-or an amature winding of a D..C.'n1otor,- sensing means connected between said field voltage generat-r ing means :and said armature voltage generating means for interrupting the voltage coupled to an armature winding whenever the magnitudeof the field voltage is belowy a predetermined value, regulating means connected 'between said field andarmature voltage generating means for causing less than the rated'valueof armature voltage to be generated over a first range of speeds of a D.C. i motor and for causing less than the rated value of eld voltage to be generated `over .a second range of speeds of a.D.-C. motor, and means'connecte'dfbetween said field Voltage generating means and said armature volt-age generating means for biasingwsaid Afield voltage generating means only partially conducting Whenever the magnitude of the armature voltage would be lexcessive for the magnitude of the fieldvoltage developed.

2; An electronic control system for a D.C. motor comprising electronic means for generating `the ratedl r1 a regulating Vdevice for causing less than the` rated value to be. generated, energizing means connected to said reguf lating means for causing less. than the rated value of armature voltage .to be generated over a first range of speeds of a DAC. motor and for causing less than the rated value of field voltage to begenerated over :a second range ofV speeds of a D.C. motor, sensing means connected between said field voltage. generating means and said armature voltage generating means forh interrupting the voltage, coupled to an armature winding whenever the magnitude of the field voltage is below a predetermined Value, and means :connected between said fieldvoltage generating means and said armature -voltage generating means for biasing saidfield voltage generating means only partially conducting whenever the magnitude of .the arm-ature voltage weuldbe excessive for the magnitude of the. field vol-tage developed.

3. An electronic control'system` for a D.- C. motor comprising electronic means jfor generating pulsating D .C. voltage for a field winding of a D.-C. motor,.elec tronic means for generating pulsating D.C. voltage for an 'armature winding Vof a D.C.. motor,' sensing means connected to the output of said Afield voltage. generating means and to .said armature voltage genenating means for opening a pair of contacts -in the output circuit of said armature voltage generating means whenever the magnitude of the field voltage is below a predetermined value, regulating means connected'between `said field and armature voltage generating means `for lcausing less than the rated value of armature voltage to be generated over a first range of speeds of a D.C. motor and for causing less than the rated value of fieldvoltage to beV aboga?? phase-shifting n i'eans'V said armature voltage said armature voltagegenerating means for opening ya i pair KVVofcontactsinvthe outputcircuit of said :armature voltage generating means wheneverthe magnitude oft-the u field voltage is below a predetermined'value, and means connected between the gridof {another lof said first .and

' second thyratrons and the output 'of-said armature volt,-

age. generating means for biasing said grid below orsubk-v stantially near the. critical firing voltage of said first or. second thyratron whenever the magnitude of the auftragl ture. voltage would be excessive for the magnitude ot't the field voltage developed.

, 6.` An electronic control system for a D.-C. motor c :iom-` prising electronic means for generating D.-C. voltage fora fieldrwinding of a D. C. motor, means for generating D.C. voltage forV an armature windingl of a D.C. motor inf` cluding a first'and a second thyratron each having a cathjode, a grid, and an anode and connected as a full wavek generated over a second range of speeds of a' -D.C

motor, andmeans connected between saidgfieldkvoltage generating means and `said armaturevoltage generating means for biasinglsaid field voltage generating means only partially conducting whenever the magnitude of the arma# ture voltage would be excessive for the magnitudey of the fiel-d voltage developed. f 1

v4. An electronic control system for a D.-C. motor comprising means for `generating D.C. voltage for a field winding of a D.-C. motor including a first and a second arc-type thyratron each having a cathode, la grid, and an anode and connected as a full-wave rectifier,

means for generating pulsating D.C. voltage for an 4 armature winding of a D.C. motor, sensing means connected to lthe output of said field voltage generating means and to said armature Voltage generating means for opening a pair of contacts in the output ycircuit of saidlarmay ture voltage generating means whenever the magnitude of the field voltage is below a predetermined value, regulatinLY means connected between said Ifield and armature voltage generating means for causing less than the rated value 4of armature voltage to be generate-d over a frstv range of speeds of a D.-'C. motor and for causing less than the rated value of fieldl Voltage to be generated, over; a second range of speeds of a D.C. motor, yand means connected between a grid of one of said first and:y second"`v` thyratrons of said field voltage generating means yand said armature voltage generating means for biasing said one of said first and second thyratrons non conducting or only partially conducting whenever the magnitude of the Iarmature voltage would be excessive orrthe magnitude of the field voltage developed.'

if; --5; An lelectronic control system for a D.C. motor'l comprising means for generating D.C. voltage fora field winding of a ll-C. motor includinga first and a second arc-type' thyratron `each having "a cathode, a' grid,

connected to the grid of oneof said first and secondj thyratrons for relaying'the firing 'of said' one of said thyratrons, regulating means' Iconnected between said rectifier, sensing means connected tothe output ofjsaid i field voltage generating means :and to saidarmature volt age generating means for opening a pair of contacts lin i the'outputcircuit of said armature voltage generatingV means whenever the magnitude of the field voltage is below a predeterminedV value, triggerl means connected to the grids of said first and second thyratrons for energizing said thyratrons, means connected to said Ytrigger means andtosaid field voltage generating means for Venergizing said trigger means substantially early in the f positive` half 4cycle of said anodes when the field voltage isjless thanthe rated value and to energize said triggery mean substantially later inirthe positivehalf cycle of said;

anodes when'the rated value of field voltage is being: generated, and means connected between said eldvoltage generating means and the output circuit of said armature` voltage generating yrneansfor biasing said field voltage` generating means only partially conducting whenever the magnitude kof the armature voltage would be excessive for the magnitude of the field voltage developed;

7. An electronic control system for a D.C.v motorcomprising means for generating the rated value of D.'C.

voltage for afield winding including a first and a second f thyratron each having a cathode, a grid, and an anode,'- means forenergizing the anodes of saidY first and secondr thyratrons-180 degrees out of phase with respect to each other, means for generating therated valuefof D.C.`

voltage for anarmature winding including a rst anda y second thyratron eachr having `a cathode, a grid, and ani.

anode, means for. energizing the anodes of said first .and

second thyratrons 180 Vdegrees out of phase with respect u ,i 'i

to each other, biasing means connected tothe grids of said first and secondthyratrons of said field voltage; 'gen'- eratingrmeans for rendering said vfirst and second'thyrat! rons inoperative fora predetermined period of time before` Q Vthe fieldrvoltage is developed, trigger meansfconnected" to the gridsiof said first and second thyratronsfof said armature voltage generating means for controlling 'the f value of armaturevolt'age generated, phase-shifting means'r connected to a grid of said first and second ythyratrons of* said field voltage -generatingmeans for controlling r4the value of field voltage generated, speed control means corinectedl to said phase-shifting means and to said trigger, means :fior energizing said trigger means to 'generate` less than the rated value of armature voltage when the rated 1 bemeen'theputput of said field voltage generating means', and the'output fof said armature voltage generating means for opening a pair of contacts inthe output of said armaor substantially near the critical voltage for firing said ture voltage generating means whenever said field voltage second thyratrons whenever said armature voltage would falls below a predetermined minimum value, and sensing be excessive for the magnitude of said eld voltage demeans connected between said armature voltage generatveloped.

ing means and the grid of said second thyratrons of said 5 eld voltage generating means for biasing said grid below No references cited' 

